Can someone please advise whether the below sentence is correct?
"Can you please help to check whether they have did the cash transfer?"
I do it every day.
I did it yesterday.
I have done it already. -- You need "done" when forming the perfect, with "have."
I had done it before he even asked.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.